1. Field of the Invention
The invention pertains to all cranes equipped with counterweight carriages, especially to large cranes with a superstructure, with at least one main boom and at least one derrick boom, and with a separate counterweight connected to the tip of the derrick boom.
2. Description of the Related Art
The invention can be used for various types of cranes. These will be explained briefly in the following. In all cases, a main boom 1 and a derrick boom 2 are hinged to a common structure, which is referred to as the superstructure 3. In the case of an inventive crane, the superstructure 3 can move with at least one degree of freedom with respect to the ground or its foundation structure. The various types of cranes differ with respect to their degrees of freedom. In the case of a mobile crane (FIG. 1), the superstructure 3 is connected rotatably to an undercarriage 4, which can travel over the ground on crawlers or wheels. In the case of an outrigger crane, the superstructure is connected rotatably to a chassis, which stands on outriggers resting on the ground or on a pontoon. Mobile cranes can also be combined with outriggers. Another type of crane is the ring-lift crane, where the superstructure rides on a ring-shaped track. The track does not necessarily have to be closed and does not even have to be circular. Other types of cranes can also be imagined, as long as the superstructure has at least one degree of freedom with respect to the ground or its foundation structure, where the term “foundation structure” is understood here to include undercarriages, outriggers, and ring-shaped tracks.
The crane shown here by way of example belongs to the prior art and is a lattice-boom crawler crane, which operates according to the derrick crane principle; that is, the basic machine is designed without ballast and makes no contribution to the stability moment.
So that large loads can be lifted, a relatively large counterweight must be provided because of the basic machine's complete or almost complete the lack of contribution to the stability moment. When the crane rotates or travels, this counterweight must be carried along, too. Known solutions include ballast arrangements which are either lifted from the ground or rest on counterweight carriages with crawlers or wheels.
The disadvantage of the non-traveling ballast arrangements is that, in the case of small-to-medium loads, it is not always possible to raise the ballast, and in the case of derrick cranes it is not usually allowable to do so.
The high ballast weights required to achieve high lifting capacities, however, require large-sized, complicated, and expensive traveling designs. For this purpose, counterweight carriages with either crawlers (Lampson) or wheels have been used so far. In addition to the approach used predominantly in the past in engineering practice, namely, to build a single carriage of appropriate size, it is also possible to use two carriages in a tandem arrangement. Both solutions are complicated, expensive, and hardly suitable for application to small cranes.
The basic idea is explained in the following on the basis of the degree of rotational freedom of a mobile crane. The explanation also applies, however, to general movement of the superstructure in a horizontal plane.
Underneath the previously mentioned derrick boom 2 there is a superlift counterweight 5. This is connected to the tip of the derrick boom 2 by the superlift carrier rods 6. The superlift carrier rods can also be designed as cables, chains, hydraulic cylinders, or other tension elements, and any desired number of them can be provided. The derrick boom 2 is connected to the main boom 1 by main boom retaining rods 7 (whether cables or rods or other tension elements are used is unimportant for the invention). A load 8 on the main boom 1 generates a force in the main boom retaining rods 7, which generates in turn a force in the superlift carrier rods 6. The superlift counterweight 5, which corresponds to the force in the superlift carrier rods (in 6), is referred to as an “activated” superlift counterweight.
So that the crane can rotate, the superlift counterweight 5 is placed on or attached to a counterweight carriage 9. The counterweight carriage has undercarriage with wheels 10 or crawlers 10a,10b. FIGS. 5 and 6 schematically show the counterweight carriage with hydraulic cylinders 20a, 20b, and reeved cables 21a, 21b, respectively, connecting the additional counterweight 16 to the crossbeam 14.